Discovery of μ-opioid selective ligands derived from 1-aminotetralin scaffolds made via metal-catalyzed ring-opening reactions

Article abstract of DOI:10.1016/j.bmcl.2008.12.095

A series of 1-aminotetralin scaffolds was synthesized via metal-catalyzed ring-opening reactions of heterobicyclic alkenes. Small libraries of amides and amines were made using the amino group of each scaffold as a handle. Screening of these libraries aga

Full text of DOI:10.1016/j.bmcl.2008.12.095

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1228–1232
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of
l-opioid selective ligands derived from 1-aminotetralin
scaffolds made via metal-catalyzed ring-opening reactions
c
c
Chris Dockendorff a, Shujuan Jin b, Madeline Olsen a, Mark Lautens a, , Martin Coupal , Lejla Hodzic ,
*
Nathan Spear d, Kemal Payza c, Christopher Walpole b, Mirosław J. Tomaszewski b,
*
a Davenport Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6
b Department of Medicinal Chemistry, AstraZeneca R&D Montréal, 7171 Frédérick-Banting, Saint-Laurent, Québec, Canada H4S 1Z9
c Department of Molecular Pharmacology, AstraZeneca R&D Montréal, Québec, Canada
d Department of Neuroscience, AstraZeneca Pharmaceuticals, 1800 Concord Pike, Wilmington, Delaware 19850-5437, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 1-aminotetralin scaffolds was synthesized via metal-catalyzed ring-opening reactions of hete-
robicyclic alkenes. Small libraries of amides and amines were made using the amino group of each scaf-
fold as a handle. Screening of these libraries against human opioid receptors led to the identification of
Received 5 November 2008
Revised 16 December 2008
Accepted 17 December 2008
Available online 30 December 2008
(S)–(S)-5.2a as a high-affinity selective
l
ligand (IC50
l
= 5 nM,
j
= 707 nM, d = 3,795 nM) displaying
M; Emax = 18%).
l-
agonist/antagonist properties due to its partial agonism (EC50 = 2.6
l
Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
Keywords:
Mu opioid ligand
Chemical library
Metal catalyzed ring opening
Opioid receptor ligands (opiates) have been used medicinally
for thousands of years, and work continues to identify and develop
selective, well-tolerated molecules for several different indications.
During the course of an ongoing search for potent and selective no-
vel opioid receptor ligands, it was recognized that tetrahydronaph-
philes,4 followed by displacement of the resulting hydroxyl groups
with azide, followed by reduction (Scheme 1). A number of devel-
opments in our labs have enabled the use of alcohol,5 carboxylate,5
phenol,5 amine,5 and sulfide6 nucleophiles with rhodium (I) cata-
lysts, which generally lead to ring-opened products of exclusive
trans stereochemistry with excellent enantioselectivities. Concur-
rently, several metals have been reported to enable ring-openings
of oxabicyclic alkenes with alkyl,7 aryl,8 and alkenyl7 nucleo-
philes,9 which generally give exclusively cis configured products.10
Subsequent to our initial synthetic studies, it was found that
ring-opening reactions of less-reactive azabenzonorbornadienes
are possible under appropriate conditions, with both hetero-
atom2,11 and carbon-based12 nucleophiles (Scheme 2). These reac-
tions have the advantage of giving a direct synthesis of 1-
aminotetralin scaffolds, in general with complementary relative
stereochemistry to the products of the sequences outlined in
Scheme 1.13 This approach has additionally been used for the syn-
thesis of several libraries not described in this communication.
According to the chemistry outlined in Schemes 1 and 2, both
di- and tetrahydronaphthalenes are accessible. Tetrahydronaph-
thalenes are generally more stable (less prone to oxidation and
elimination reactions), but several examples of dihydronaphtha-
lene scaffolds were used for library synthesis. In the reactions out-
lined in Scheme 2, hydrogenation of the olefin generally preceeds
deprotection, except in the case of nosyl-protected products.
With scaffolds of types 4.1–4.6 in hand (Schemes 1 and 2), we
prepared a number of secondary scaffolds by acylating the amine
thalenes (tetralins) such as the
j
-agonist 11 (Scheme 2) could be
conveniently accessed by new metal-catalyzed ring-opening meth-
ods developed in our labs.2 A variety of other tetralins also have
important and diverse bioactivities, including morphine, sertraline,
and podophyllotoxin. We were thus inspired to initiate a program
to synthesize gram-scale quantities of 1,2-disubstituted tetralin
scaffolds which could be utilized in drug discovery efforts. This pa-
per describes the synthesis of several of these scaffolds and their
application in library synthesis, which has led to the identification
of a selective and high-affinity
l-opioid receptor ligand with low
l
-efficacy. Such compounds are clinically important as analgesics
(e.g., meperidine (DemerolÒ) and dezocine (DalganÒ)), and for
the treatment of drug addiction (e.g., methadone and
buprenorphine3).
At the outset of this project, we decided to focus on making 1-
aminotetralin scaffolds with diverse substitution patterns and ste-
reochemistry. We accessed these structures via rhodium-catalyzed
ring-opening of oxabenzonorbornadienes with a variety of nucleo-
* Corresponding authors. Tel.: +1 416 978 6083; fax: +1 416 946 8185 (M.L.).
E-mail addresses: mlautens@chem.utoronto.ca (M. Lautens), mirek.tomaszewski@
astrazeneca.com (M.J. Tomaszewski).
0960-894X/$ - see front matter Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.12.095

C. Dockendorff et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1228–1232
1229
X
X
Nu
Nu
4.1
3.1
NuH or R-M
1. reduce olefin
2. displace with
azide
OH
NH2
O
X
(trans isomer (4.4) if NuH =
amine)
Rh(I) cat.
or Pd(II) cat. (R-M only)
base, additive
3. reduce azide
2.1
NuH = alcohol, amine, sulfide,
malonate, phenol, carboxylate
X
X
R
R
R-M = e.g. organoboron, dialkylzinc,
alkylzinc halide
3.2
4.2
NH2
OH
R = alkyl, aryl, alkenyl
Scheme 1. Synthesis of 1-aminotetralin ligands via ring-opening of oxabicylic alkenes.
X
X
X
N
Nu
R
Nu
1. deprotect
2. reduce olefin
(optional)
N
NuH or R-M
NHPG
NH2
Cl
Cl
NPG
X
3.3
4.3 = dihydronaphthalene
4.4 = tetrahydronaphthalene
Rh(I) cat.
or Pd(II) cat. (R-M only)
base, additive
O
1
(these operations
may be inverted)
2.2
(previously reported)
NuH = alcohol, amine, sulfide,
malonate, phenol, carboxylate
X
R
NHPG
R-M = currently organoboron
R = currently aryl
NH2
3.4
4.5 = dihydronaphthalene
4.6 = tetrahydronaphthalene
PG = Boc or Ns (2- or 4-NO2PhSO2-)
Scheme 2. Synthesis of 1-aminotetralin ligands via ring-opening of azabicylic alkenes.
moieties with several acid chlorides and reducing the resulting
amide carbonyl groups with alane (AlH3).14 These were then acyl-
ated with a set of commercially available acid chlorides to give a
series of focused libraries (Scheme 3). A selection of racemic com-
pounds of types 5.1–5.6 was made, along with amide libraries
composed of compounds of types 6.1–6.6. These were screened
against cloned human opioid receptors. Initial screening was per-
philes have often been problematic due to insertion of the rhodium
into one of the aromatic C–H bonds from a catalytic intermediate
after addition of Rh–Ar across the olefin, which leads to unopened
and/or oligomeric adducts.15 However, we were pleased to find
that in this case the ring-opening reaction with thiophene-3-boro-
nic acid proceeded in moderate yield with excellent enantioselec-
tivity using the Josiphos-type ligand PPF-P(t-Bu)2, in accordance
with our original report.8b The intermediate dihydronaphthalene
was hydrogenated using diimide generated in-situ from the oxida-
tion (NaIO4) of hydrazine, giving the cis-tetrahydronaphthol 3.2a.
Mitsunobu inversion proceeded to give azide 3.2b in moderate
yield. Staudinger reduction of 3.2b with PPh3 in THF with an excess
of water proceeded quantitatively, and the resulting crude amine
4.2a was acylated to give amide 4.2b. An X-ray crystal structure
of this intermediate confirmed the expected absolute configura-
tion.16 Reduction with alane14 gave the desired single enantiomers
of 5.2a in excellent yield.
formed at a concentration of 10 lM for each library member. Com-
petitive binding studies with standard radiolabelled ligands were
used for each receptor. Compounds showing greater than 50% inhi-
bition were re-synthesized, purified and underwent further mea-
surements to calculate IC50 values, of which selected results are
presented in Table 1.
Prompted by the initial screening results (vide infra), we re-syn-
thesized compounds 5.2a and 6.3f in enantiopure form, which pro-
vide good illustrations of the specific synthetic sequences
discussed in general terms previously. The single enantiomers of
5.2a were made as outlined in Scheme 4. We have found that the
rhodium-catalyzed ring-opening reactions with heteroaryl nucleo-
The synthesis of the enantiomers of 6.3f (Scheme 5) began with
the Rh-catalyzed asymmetric ring-opening of N-Boc azabenzonor-
X
X
X
Nu
Nu
O
Nu
Z-COCl (1.4 eq.)
NEt3 (1.2 eq.)
CH2Cl2, rt
1.Y-COCl (1.4 eq.)
NH2
N
Y
HN
Y
NEt3 (1.2 eq.)
CH2Cl2 rt
Z
2. AlH3 (3 eq.)
THF, 0 °C to rt
X
X
X
R
R
O
R
NH2
N
Y
HN
Y
4.1 to 4.6
6.1 to 6.6
Z
5.1 to 5.6
Scheme 3. Functionaliztion of 1-aminotetralins and library synthesis.

1230
C. Dockendorff et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1228–1232
Table 1
Binding and
l functional data for selected compounds active against human opioid receptors
Compound
l
IC50
j
IC50
d IC50
l
EC50
l
Compound
l
IC50
j
IC50
d IC50
l
EC50
l
(nM)
(nM)
(nM)
(nM)
Emax
(nM)
(nM)
(nM)
(nM)
Emax
(%)
(%)
N
PhN
N
O
O
(+/-)
(+/-)
(+/-)
69
2209 7161
>90,000 15
181
7993
1955 >90,000
0
HN
5.2a
S
S
O
O
O
6.3e
Cl
N
O
5.3
707 3795
2600
18
100
7136
2289 >90,000
0
PhN
N
S
HN
(S)-(S)-5.2a
Cl
6.3f
N
PhN
N
O
N
N
O
S
4862
>10,000 1274
N.T.
N.T.
58
1324
1243 N.T.
N.T.
(+/-)
Cl
O
S
O
6.2a
N
(R)-(R)-6.3f
O
N
O
N
O
N
PhN
N
O
O
O
126
>10,000 3947
>90000
5
245
155
>10,000 >90,000
0
(+/-)
(+/-)
O
O
6.4g
6.3a
Cl
O
O
N
O
N
PhN
N
O
N
O
443
>10,000 3620
>90,000 60
351
6002
3501 >90,000
0
(+/-)
(+/-)
O
6.3b
Cl
Cl
6.4h
Cl
Cl
O
O
N
O
N
O
PhN
N
O
O
N
O
211
6121 3887
>90,000 10
1122
922
>10,000 >90,000
0
(+/-)
Cl
(+/-)
6.3c
Ph
6.i
O
O
N
O
N
O
(+/-)
PhN
N
O
N
151
>10,000 1467
>90,000 10
4828
1005
>10,000 N.T.
N.T.
(+/-)
O
O
Br
6.3d
6.j
All compounds are P95% pure. Inhibition binding assays were performed against [125I]-FK33824, [125I]-deltorphin II, and [125I]-U69593 for
l, d, and j, respectively.Values are
means of 3 measurements. N.T., not tested.

C. Dockendorff et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1228–1232
1231
S
O
(1.2 eq.)
1.
DEAD, DPPA
PPh3 (1.2 eq. each)
B(OH)2
toluene, -8 °C to rt
2.1a
OH
[Rh(COD)Cl]2(2.5%)
(R)-(S)-PPF-P(t-Bu)2 (5%)
Cs2CO3/H2O
THF, rt
3.2a
S
N3
S
63%
3 mmol
3.2b
55%, >99% ee
2. HN=NH
O
O
Cl
AlH3
PPh3
THF
NEt3, DCM
0 °C to rt
THF/H2O
1. rt, 12 h
2. 60 °C, 1 h
HN
HN
S
4.2a
NH2
S
S
O
O
(S)-(S)-5.2a
90%
O
4.2b
93% (2 steps)
enantiomeric series also completed
x-ray structure obtained
confirming absolute stereochemistry
Scheme 4. Enantioselective synthesis of 5.2a.
Boc
PhN
NH
(5 eq.)
N
TFA
N
N
DCM/MeOH
[Rh(COD)Cl]2 (2.5%)
PPF-P(t-Bu)2 (5 %)
110 °C, 60 h
PhN
NHBoc
PhN
NH2
4.3f
62%, 94% ee
>99% ee after recryst.
from EtOH
2.2
a
.
3.3f
O
S
Cl
O
N
O
Cl
Cl
N
PhN
N
O
PhN
HN
NEt3
DCM
0 °C to rt
O
1. NEt3
Cl
O
DCM, 0 °C to rt
2.AlH3 (3 eq.)
THF, 0 °C to rt
(R)-(R)-6.3f
57% (3 steps)
5.3f
S
enantiomeric series also completed
Scheme 5. Enantioselective synthesis of 6.3f.
bornadiene 2.2a with N-phenylpiperazine, using PPF-P(t-Bu)2 as li-
gand. Dihydronaphthalene 3.3f was obtained in 62% yield, 94% ee,
and >99% ee after recrystallization. It was necessary to heat the
reaction in neat N-phenylpiperazine at 110 °C for an extended per-
iod (60 h) for good conversion. Since this work was performed, our
lab has reported improved results (92%,93% ee) using C2-Ferriphos
as the ligand.11 Deprotection with TFA, acylation with methoxyace-
tyl chloride, reduction of the intermediate amide with alane, and
acylation with 3-chlorothiophene-2-carbonyl chloride proceeded
smoothly to give the individual enantiomers of 6.3f.
the l-opioid receptor (IC50 = 69 nM) and selectivity versus d- and
j-opioid receptors (>30-fold).
We were pleased to observe that the (S)–(S) enantiomer of 5.2a
(IC50
mer of 6.3f (IC50
l
= 5 nM,
j
= 707 nM, d = 3795 nM) and the (R)–(R) enantio-
= 58 nM, = 1324 nM, d = 1243 nM,) both dis-
l
j
played high affinity and excellent selectivity for the human
l-
opioid receptor.17
Selected compounds in Table 1 were tested for agonist activity
-receptor, using [35S]-GTP
S binding as the func-
at the human
l
c
tional endpoint, as described elsewhere.18,19 Compound 5.2a dis-
played measurable agonist efficacy. Its weak EC50, shifted to the
right compared to its IC50, may be due at least in part to the
requirement of sodium in the functional assay (sodium decreases
the affinity of opioid agonists20). The more active enantiomer,
Binding and
given in Table 1. The N-phenylpiperazine dihydronaphthalenes
(6.3a-6.3f) are -selective ligands that are weakly sensitive to
the acyl side chain employed, with potencies ranging from
100–440 nM. The most potent and selective compound from this
subclass is 6.3f which shows IC50 of 100 nM and is >20-fold
selective versus and d-opioid receptors. In the case of dimethyl-
amino analogues (6.4g-6.4j) with the tetrahydronaphthalene core,
affinity was found to be sensitive to the acyl side chain employed
(e.g., 6.4g and 6.4h vs. 6.4i and 6.4j). Moreover, depending on the
acyl group, it is possible to introduce activity at the -opioid recep-
tor thereby affording mixed activity (e.g., 6.4g). Overall, tetra-
l functional data for selected tetralin compounds is
l
l
(S)–(S)-5.2a, was characterized further by [35S]-GTP
say. (S)–(S)-5.2a yielded low efficacy (Emax 18% at 100
EC50 = 2.6 M), and was shown to reverse DAMGO in a dose depen-
cS binding as-
l
lM;
j
l
dent manner, down to the level of its own intrinsic efficacy (Fig. 1).
In summary, we have utilized several metal-catalyzed ring-
opening reactions developed in our laboratories to synthesize a
variety of 1-aminotetralin-type scaffolds. Several examples of rho-
dium-catalyzed additions of carbon and heteroatom nucleophiles
to heterobicyclic alkenes were presented. These scaffolds were
used to make libraries of amines and amides, which have been
l
j
l/j
lin 5.2a, derived from the ring-opening of oxabenzonorbornadiene
with thiophene-3-boronic acid, showed the most active binding to

1232
C. Dockendorff et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1228–1232
References and notes
110
90
70
50
30
10
-10
1. (a) Freeman, J. P.; Michalson, E. T.; D’Andrea, S. V.; Baczynskyj, L.; Von
Voigtlander, P. F.; Lahti, R. A.; Smith, M. W.; Lawson, C. F.; Scahill, T. A.; Mizsak,
S. A.; Szmuszkovicz, J. J. Med. Chem. 1991, 34, 1891; (b) Rajagopalan, P.;
Scribner, R. M.; Pennev, P.; Schmidt, W. K.; Tam, S. W.; Steinfels, G. F.; Cook, L.
Bioorg. Med. Chem. Lett. 1992, 2, 715.
DAMGO (163nM)
(S)-(S)-5.2a (EC50 2.6µM; Emax 18%)
(S)-(S)-5.2a reversal of DAMGO (300nM)
(app. IC50: 19µM)
2. Lautens, M.; Fagnou, K.; Zunic, V. Org. Lett. 2002, 4, 3465.
3. Buprenorphine is a partial mu agonist used in both analgesia and the treatment
of heroin addiction. See for example Tzschentke, T. M. Psychopharmacology
2002, 161, 1.
4. (a) Lautens, M.; Fagnou, K.; Hiebert, S. Acc. Chem. Res. 2003, 36, 48; (b) Lautens,
M.; Fagnou, K.; Yang, D. J. Am. Chem. Soc. 2003, 125, 14884.
(S)-(S)-5.2a intrinsic efficacy
-3
-9
-8
-7
-6
-5
-4
Log M
5. See Ref. 4 and references therein.
6. Leong, P.; Lautens, M. J. Org. Chem. 2004, 69, 2194.
Figure 1. Reversal of DAMGO by (S)–(S)-5.2a in
Average of two experiments performed in duplicate. Data points are displayed as
the arithmetic mean value SD; maximal effect (100%) is relative to DAMGO
a [ cS binding assay.
35S]-GTP
7. For selected examples, see Ref. 4a and references therein, as well as: Scope
studies (a) Lautens, M.; Hiebert, S. J. Am. Chem. Soc. 2004, 126, 1437;
Application in total synthesis (b) Lautens, M.; Colucci, J. T.; Hiebert, S.; Smith,
N. D.; Bouchain, G. Org. Lett. 2002, 4, 1879; (c) Mechanism: Lautens, M.;
Hiebert, S.; Renaud, J. -L. 2001, 123, 6834.; With organozinc halides (d) Zhang,
T. K.; Yuan, K.; Hou, X.-L. J. Organomet. Chem. 2007, 692, 1912.
(30 lM).
8. (a) Murakami, M.; Igawa, H. Chem. Comm. 2002, 390; (b) Lautens, M.;
Dockendorff, C.; Fagnou, K.; Malicki, A. Org. Lett. 2002, 4, 1311.
screened against cloned human opioid receptors. The high-affinity
-selective ligand (S)–(S)-5.2a emerged as a molecule displaying
partial -agonist/antagonist properties. The maximal effect of
(S)–(S)-5.2a as a partial agonist on human -opioid receptor-med-
iated [35S]-GTP
S binding (18% Emax, with EC50 = 2.6 M) was
slightly below that of meperidine (28% Emax and 9.4
M EC50).19
However, we found that (S)–(S)-5.2a had higher -efficacy than
the clinically used -opioid partial agonist dezocine, which showed
only 6% Emax and 38 nM EC50 in our
9. It should also be noted that Cheng and coworkers have synthesized a variety of
dihydronaphthalenes from metal-catalyzed ring-opening reactions with
electrophilic partners (e.g. aryl halides) under reductive conditions. See for
example (a) Wu, M.-S.; Rayabarapu, D. K.; Cheng, C.-H. J. Org. Chem. 2004, 69,
8407. and references therein; For variations reported by Martin, see (b) Chen,
C.-L.; Martin, S. F. J. Org. Chem. 2006, 71, 4810. and references therein.
10. An exception is the Cu-catalyzed alkylative ring-opening reactions reported by
Feringa which provide selectively trans adducts Bertozzi, F.; Pineschi, M.;
Macchia, F.; Arnold, L. A.; Minnaard, A.; Feringa, B. L. Org. Lett. 2002, 4, 2703; See
also Zhang, W.; Wang, L.-X.; Shi, W.-J.; Zhou, Q.-L. J. Org. Chem. 2005, 70, 3734.
11. Cho, Y.-H.; Zunic, V.; Senboku, H.; Olsen, M.; Lautens, M. J. Am. Chem. Soc. 2006,
128, 6837.
12. See for example (a) Lautens, M.; Hiebert, S.; Renaud, J.-L. Org. Lett. 2000, 2,
1971; (b) Lautens, M.; Dockendorff, C. Org. Lett. 2003, 5, 3695; (c) Carretero, J.
C.; Cabrera, S.; Arrayás, R. G. Angew. Chem. Int. Ed. 2004, 43, 3944; (d) Arrayás,
R. G.; Cabrera, S.; Carretero, J. C. Org. Lett. 2005, 7, 219; (e) Arrayás, R. G.;
Cabrera, S.; Carretero, J. C. Synthesis 2006, 1205; (f) McManus, H. A.; Fleming,
M. J.; Lautens, M. Angew. Chem. Int. Ed. 2007, 46, 433.
l
l
l
c
l
l
l
l
l [ cS functional as-
35S]-GTP
say).21 Drugs with a similar profile have proved beneficial in the
treatment of pain as well as for the treatment of drug addiction,
particularly due to their low dependence-inducing potential.3
Acknowledgments
13. An exception involves the ring-opening of oxabenzonorbornadienes with
secondary amines. Displacement of the resulting hydroxyl group proceeds
with retention of configuration, thus only trans products are normally
accessible via this sequence. See: Lautens, M.; Schmid, G. A.; Chau, A. J. Org.
Chem. 2002, 67, 8043.
We thank Dr. Keith Fagnou, Dr. Valentin Zunic, Dr. Gavin Sch-
mid, Dr. Bernard LeRoy, Rohan Brown, Obinna Onuora, Karine Pal-
cy, Alena Rudolph, and Dr. Hisanori Senboku, who made one or
more aminotetralin scaffolds used in these or other unpublished
studies, and who helped to develop the methods used here. We
also thank Dr. Yong-Hwan Cho for re-synthesizing some additional
material needed for our studies, Dr. Tim Burrow (NMR), Dr. Alan
Lough (X-ray), and Dr. Alex Young (MS) for analytical support.
We are also grateful to NSERC, the University of Toronto, and the
W.C. Sumner foundation (fellowship for C.D.) for funding this re-
search, and to Sovias AG for providing the PPF-P(t-Bu)2 ligand used
in this work.
14. (a) Brown, H. C.; Yoon, N. M. J. Am. Chem. Soc. 1968, 90, 2927; (b) Cha, J. S.;
Brown, H. C. J. Org. Chem. 1993, 58, 3974.
15. (a) Dockendorff, C.; Lautens, M.; Lough, A. J. Acta Cryst. 2006, E62, o1601; (b)
Oguma, K.; Miura, M.; Satoh, T.; Nomura, M. J. Am. Chem. Soc. 2000, 122, 10464;
(c) Menard, F.; Lautens, M. Angew. Chem. Int. Ed. 2008, 47, 2085.
16. Dockendorff, C.; Lautens, M.; Lough, A. J. Acta Cryst. 2006, E62, o639 (X-ray
coordinates were also deposited in the Cambridge Crystallographic Data
Centre, deposition number 298396).
17. The IC50 at the
l-receptor for (S)–(S)-6.3f = 2.8 lM, and for (R)–(R)-5.2a = 772 nM.
18. The methods used to determine receptor binding and function values were
similar to those used in previous reports by AstraZeneca. See Plobeck, N. et al J.
Med. Chem. 2000, 43, 3878.
19. K. Payza, Binding and activity of opioid ligands at the cloned human delta, mu,
and kappa receptors. In The Delta Receptor; K. -J. Chang, F. Porreca, J. H. Woods,
Eds.; Marcel Dekker, New York, pp. 261.
Supplementary data
20. Pfeiffer, A.; Sadée, W.; Herz, A. J. Neurosci. 1982, 2, 912.
21. Payza, K.; St-Onge, S.; LaBarre, M.; Godbout, C.; Wahlestedt, C. Abstracts of
Papers, 26th Annual Meeting of the Society of Neuroscience; Washington, DC;
1996 (Abstract 695.14).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2008.12.095.